Immigrants often have lower rates of obesity compared to their U.S. born counterparts. However, over time, rates of obesity rise among immigrants and converge to the U.S. born. This rise among immigrants is often attributed to acculturation, referring to the adoption of American behaviors and norms. Yet, globalization has spurred the marketing and adoption of American goods and practices across the world, and rates of obesity are rising worldwide. These observations raise questions about secular trends and imply the counterfactual of whether immigrants would have gained weight without migration. Studies of immigrants often fail to address the issues of secular trends and global changes because they are not designed to do so. To study these issues, we propose three specific aims: (1) to conduct a dual- cohort prospective, transnational study; (2) compare changes in obesity risk factors between two cohorts; (3) examine the mediators and moderators of change in obesity risk for both cohorts. This study proposes to prospectively follow two cohorts of adults for three years. The first cohort of migrants (n=800) will be followed from the Philippines to the United States. The second cohort of non-migrants (n=800) will be followed within the Philippines. The use of a dual cohort design is analogous to a natural experiment with migration as the treatment. Migrants will be sampled from participants attending a mandatory seminar offered by the Commission for Filipinos Overseas (CFO), the Philippines governmental agency that regulates all legal permanent migration from the country. Our unique relationship with the CFO allows us the ability to assess migrants 1-2 months prior to emigration to the U.S. This provides novel information about migrants that have not been previously available. Migrants will be sampled from a list of migrants attending mandatory CFO training sessions. Non- migrants will be sampled using stratified sampling of persons living in the areas of Metropolitan Manila and Cebu, Philippines. Non-migrants will be assessed annually, for a total of 4 waves of data (baseline, year 1, year 2, year 3); migrants will be assessed in the same way, plus one additional assessment 2-3 months after entry into the U.S. We will measure anthropometrics, biomarkers through dried blood spots, dietary and physical activity, and administer a survey. Statistical analyses will include linear mixed effects models to assess the trajectories over time (Aim 1), mediation analyses (Aim 2), and tests of moderation (Aim 3). We will use propensity score matching to reduce bias due to confounding. The results of this study will provide rare and unique information about the pre-migration experiences of emigrants, provide rigorous a test of secular trends versus acculturation, evaluate a novel conceptual framework, and provide valuable information from which to develop prevention efforts to reduce the burden of obesity and related conditions among an important immigrant population.